The aim of this project is to determine the role of striatal dopamine release in motivation and reinforcement. Recently, we found that chemical stimulation of the supramammillary nucleus is reinforcing in rats, suggesting that the supramammillary nucleus may be a component of primary reinforcement. Since dopamine release in the ventral striatum has been implicated in primary reinforcement, we examined whether electrical stimulation of supramammillary nucleus is reinforcing and evokes dopamine release in the ventral striatum as shown by voltammetric signals. Rats learned to lever-press to deliver brief trains of electrical stimulation at the supramammillary nucleus with currents around 200 micro A. Electrical trains that support vigorous self-stimulation at the supramammillary area induced dopamine released as indicated by voltammetric signals. Temporal patterns of dopamine signals evoked by supramammillary stimulation are essentially identical to those of evoked by ventral tegmental stimulation. These results suggest that supramammillary stimulation triggers dopamine release in the ventral striatum, which has been implicated in primary reinforcement, and that the supramammillary nucleus is part of the reward circuitry associated with the meso-limbic dopamine system.